Columns foundations need strengthening in the case of applying additional loads. Widening and strengthening of existing foundations may be carried out by constructing a concrete jacket to the existing footings. The new jacket hould be properly anchored to the existing footing and column neck in order o guarantee proper transfer of loads. The size of the "jacket" shall be selected such that the average maximum foundation pressure does not exceed the recommended allowable value. Attention shall be given during construction in rder that the excavations for the new "jackets" do not affect the existing djacent foundations.
An isolated footing is strengthened by increasing the size of the footing and the reinforcement steel bars as follows:
1. Excavating around the footing
2. Cleaning and roughening the concrete surface.
3. Installing dowels at 25-30cm spacing in both directions using an appropriate epoxy material.
4. Fastening the new steel bars with the dowels using steel wires. The diameter and number of steel bars should be according to the design.
5. Coating the footing surface with a bonding agent in order to achieve the equired bond between old and new concrete.
6. Pouring the new concrete before the bonding agent dries. The new oncrete should contain a non-shrinkage material.
The previous steps are illustrated in Fig 1.
Fig.1: Steps for strengthening foundations
The following photos (13-16) illustrate the practical way of jacketing a footing by reinforced concrete.